Ionic equilibria, selectivity and diffusion of cations in soils as influenced by calcium and magnesium

Abstract

Abstract Four Indiana soils were used to study the changes in ionic equilibria, selectivity and effective diffusion coefficient of cations at five levels of Ca and Mg. In all the soils, adsorption isotherms for Ca and Mg differred Indicating variation in the nature of exchanger involved. Addition of Ca and Mg reduced the fractional saturation of monovalent cations in solution and exchange phase. However, no such conclusions could be drawn for divalent cations. In all the soils, Rb is preferentially adsorbed over K and Na. In all the soils, increasing levels of Ca and Mg reduced the magnitude of the selectivity coefficient for homovalent ion pairs (Rb/Na, K/Na) and mono‐divalent ion pairs (Rb/Ca, Rb/Mg, K/Ca, K/Mg, Na/Ca, Na/Mg). These changes in selectivity coefficient are attributed to fractional saturation changes on the exchanger and differences in the free energy of hydration of the two counter ions involved. In all the four soils addition of Ca ang Mg increased the effective diffusion coefficient of ...